Image display panels for displaying monochromatic images or color images comprise plasma display panels (PDP). Panels of this type are used, for example, as displays for televisions and computer applications. In a plasma display panel, the plasma generates UV radiation exciting electroluminescent phosphors. The luminous flux of such a panel is substantially isotropic.
An image display panel of the type described in the opening paragraph is known from, for example, German Offenlegungsschrift DE 3016810. The image display panel described herein is provided with an array of cylindrical lenses situated at the area of a row of discharge pixels of the panel on the viewer""s side of the panel. The light rays coming from the image display panel are concentrated within a given viewing angle perpendicular to the image display panel. In addition to a sufficient brightness of the image display panel, it is important that the light emitted by the image display panel also falls within the correct viewing angle. A correct viewing angle is understood to mean the viewing angle within which the viewers are present. Light falling outside this viewing angle is thus lost to the viewers.
In the known image display panel, there is one cylindrical lens per row of discharge pixels, and the axis of the cylindrical lens is situated above the center of the corresponding row of discharge pixels.
A drawback in this case is that the light will be concentrated right in front of the image display panel. Dependent on the use of the panel and, consequently, on the viewer""s position with respect to this panel, the viewer will observe an uneven distribution of the intensity across the image.
It is an object of the present invention to provide an image display panel having a viewing angle which is limited in size but is sufficiently large, and in which the intensity variation across the image is considerably reduced for the viewer.
According to the invention, the image display panel, in which the pitch of the cylindrical lens array is equal to the pitch of the image cells, is therefore characterized in that the cylindrical lens array is shifted with respect to the image cells in a direction substantially perpendicular to the second electrodes.
By shifting the cylindrical lens array in said direction with respect to the row of discharge pixels, the viewing angle will be spatially shifted. In fact, in many applications, a viewer is not present right in front of the image display panel but slightly lower than the panel. This applies both to domestic use and to uses of large screens in public establishments. Due to the above-mentioned measure, the viewing angle limited by the cylindrical lens array is spatially shifted. For example, a shift such that the image reaches the image display panel at an angle of 15xc2x0 to 20xc2x0 with respect to the direction perpendicular to this panel yields an image having a much higher light intensity within the relevant viewing angle for the viewer as compared with the case where the cylindrical lenses are present exactly above the rows of discharge pixels.
Another embodiment of the image display panel according to the invention is characterized in that the cylindrical lens array has a smaller pitch than the image cells.
The pitch of the image cells is understood to mean the vertical pitch when the image display panel is in use.
By adapting the pitch of the cylindrical lens array, the distance to the panel on which the brightness and light homogeneity of the image is optimal can be adapted. The size of the pitch of the cylindrical lens array defines this distance.
A preferred embodiment of the image display panel according to the invention is characterized in that the cylindrical lens array is shifted with respect to the image cells in a direction substantially perpendicular to the second electrodes.
By shifting both the cylindrical lens array with respect to the rows of discharge pixels and making the pitch of the cylindrical lenses smaller than the pitch between the discharge pixels, the light rays coming from the image display panel can be directed and the light intensity can be concentrated. In this way, the light intensity will be relatively high for the viewers and the intensity variation across the image display panel is reduced to a minimum.
A further embodiment of the image display panel according to the invention is characterized in that the cylindrical lens array is implemented as a separate element, with the cylindrical lens structure facing the image display panel. In addition to the optical shift, the array may also play the role of a protective plate for the panel if mechanical defects should occur. When, moreover, the lens structure faces the image display panel, the lens structure is prevented from being contaminated by, inter alia, dust and fingerprints. In this case, the outer side of the panel may be a smooth surface which may also be provided with coatings in a relatively simple way.
Another embodiment of the image display panel according to the invention is characterized in that the cylindrical lens array is provided on a side of the first substrate facing the image display panel.
This has the advantage that the cylindrical lens array does not need to be implemented as a separate element in this case but forms part of the glass plate used as a substrate.
A further embodiment of the image display panel according to the invention is characterized in that light-absorbing material is provided between the cylindrical lens array and the image display panel at the area of the boundary faces between two successive cylindrical lenses.
By providing light-absorbing material at the area of the boundary face of two successive cylindrical lenses, for example, in the form of black lines, Moirxc3xa9 interference between the lens structure and the cell structure is prevented. Moreover, the contrast is enhanced because a part of the incident ambient light will be absorbed by the line pattern.
A further embodiment of the image display panel according to the invention is characterized in that the cylindrical lenses are implemented as Fresnel lenses.
A Fresnel structure has the advantage that it can be replicated in a relatively simple manner.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.